Axisymmetric variable flow area exhaust nozzles for gas turbine engines typically comprise a plurality of individual flaps arranged circumferentially to define a divergent exhaust duct. Each flap is hinged at the forward end, with the trailing edge movable radially for establishing a selected exhaust duct configuration. A plurality of elongated gas seals are disposed circumferentially between the hinged flaps, with a portion of each seal disposed within the exhaust duct for spanning the varying gap between adjacent flaps, and secured in place by one or more clamp components which lie outside of the duct and contact the radially outward facing surfaces of the sealed adjacent flaps.
The clamps hold the linear seal radially while allowing the seal and adjacent flaps to slide relative to each other as the nozzle is reconfigured between divergent to convergent configurations. Such clamps are therefore subject not only to repeated stress cycling depending on the flow regime of the exhaust gases within the duct, but also experience frictional wear at the surfaces which contact the respective nozzle flaps.
Prior art one piece clamp components, secured to a threaded stud and mounting plate extending from a longitudinal stiffening rib in the radially outward side of the seal include an antirotation channel welded to the clamp and engaging the mounting plate to prevent rotation of the clamp about the central securing stud. This has proved unsatisfactory during extended use cycling as the localized depletion of material properties near the weld site reduces the resistance to cracking due to fatigue. Cracking initiated adjacent the weld site can result in complete separation of a portion of the clamp and loss of effectiveness in securing the elongated flap seal.
Rubbing between the clamp and radially outer flap surfaces causes wearing of the clamp, requiring replacement of the entire component. Hardfacing of the contacting surfaces reduces the frequency of replacement, but adds additional cost to the clamp fabrication.
A third problem with the prior art one piece design occurs during periods of nozzle operation wherein a rapidly fluctuating internal duct pressure occurred. Should such pressure fluctuation coincide with the natural frequency of the one piece clamp, the clamp component will begin to vibrate rapidly, increasing frictional wear and inducing a high cycle material fatigue in the clamp structure. What is needed is a clamp assembly resistant to frictional wearing, which includes a non-welded antirotation means, and which has internal damping to avoid vibration during periods of fluctuating duct pressure.